Sep. 04, 2013

At nearly half past three on August 17, 2013, what has become one of California’s largest wildfires ignited just east of the town of Groveland, near Yosemite National Park. As of this morning, it had burned more than 237,000 acres, according to CalFire’s website, and was 80 percent contained.

NASA acquired the digital image above, revealing extensive, brownish smoke emanating from the fire, on August 23, 2013 using an instrument called the Multi-angle Imaging SpectroRadiometer, or MISR. As it flies aboard NASA’s Terra spacecraft, MISR helps keep tabs on Earth’s climate by imaging how sunlight scatters across the planet.

To capture those images, the instrument uses nine different cameras pointed in as many directions. Over seven minute periods, they successively snap away at 250-mile swaths of Earth. Each camera is also equipped with filters that collect light in four wavelengths—red, blue, green, and near infrared. Because the cameras are angled differently and have several filters, they snag slightly different views of the same point (see illustration)—views that, assembled together or compared with one another through sophisticated computerized processing techniques, provide a tapestry of information. For instance, using MISR data, researchers can learn more about various environmental components that impact climate and air quality—namely, atmospheric particles, or aerosols, cloud formations, and land surface covers (think vegetation or ice)—based on the way the way they reflect light when viewed from different camera angles.

While the image above was taken with just one of MISR’s cameras—the “nadir camera,” which points straight down—the shot below was generated by combining images from three of MISR’s cameras in a stereoscopic fashion, according to David Diner, principal investigator for the MISR experiment. Taken together, they gave researchers a 3D-like picture of the plume, allowing them to determine its height.

The Rim Fire’s billow is just one of thousands of smoke plumes that MISR has observed, according to Diner. Researchers are using such data to model how smoke rises and disperses, which can help inform how air quality might be affected, he says. Smoke from the Rim Fire, for instance, led to air quality alerts in Nevada, according to news reports.

Built to survive for six years, MISR is now pushing towards 14 years in orbit. “Knock on wood,” says Diner, it’s got more years in it yet.